1. Field of the Invention
The present invention relates generally to a display unit for an automobile or other vehicle, and more particularly to a display unit incorporating a dial of a revolution indicator such as a tachometer and a speedometer and a display device such as an LCD unit arranged at the center of the dial.
2. Description of the Related Art
A dial of a revolution indicator and a display device arranged on the surface of the dial are commonly used in a known display unit of an automobile or other vehicle. Such design is most often intended to ensure good visibility of the display device regardless of the presence of an indicating needle that points to a scale of the dial and while allowing the display device to be arranged at the center of the dial.
In a case where the dial is designed to indicate important content of information such as a vehicle speed while the display device indicates less important information such as current time, there is a need to improve such arrangement of the dial. More specifically, raising the dial relative to the central display device allows the dial to be closer to an eye point of a driver than the central display device, and thus improves the visibility of the dial.
In view of such requirement, there exists a known display unit as shown in FIGS. 4 and 5 (see for example Japanese Patent Application Laid-Open Publication No. 2005-181301). As shown in FIGS. 4 and 5, a display unit 1 includes a liquid crystal display (LCD) 2 as a display device, a dial assembly 3, a main board 4, a motor 5, an indicating needle 6, an LED light source 10, and a prism 11. The LCD device 2 is substantially circular when viewed from the eye point of the driver, and information such as warning and current time is indicated on the LCD device 2. The LCD device 2 includes a body 21, an LED light source 22 for backlighting provided on the main board 4, and a light-guiding plate 23 that guides a light beam emitted by the LED light source 22 toward an underside of the body 21.
The dial assembly 3 takes a shape of a ring (or an arc) when viewed en face by a driver, with a substantially circular hole being provided at its center. Scales and numerals are formed on the periphery of the dial assembly 3. The dial assembly 3 is provided on the front side of the LCD device 2 such that the LCD device 2 can be viewed by the driver via the hole.
The main board 4 is provided below the LCD device 2. The motor 5 has a body 51 provided on an underside of the main board 4. The motor 5 has a shaft 52 protruding on a front surface of the main board 4.
One end of the indicating needle 6 is secured to the shaft 52. The indicating needle 6 horizontally extends from the shaft 52 along the underside of the LCD device 2, bends at a right angle and vertically extends past the edge of the LCD device 2, again bends at a right angle to extend in a space between the LCD device 2 and the dial assembly 3, further bends at a right angle to vertically extend past the inner edge of the dial assembly 3, and again bends at a right angle to extend horizontally with the other end (i.e., needle portion 64) of the indicating needle 6 is positioned on the front surface of the dial assembly 3 so that the indicating needle 6 does not obstruct a line of sight between the eye point of the driver and a display area of the LCD device 2. The above-described configuration of the indicating needle 6 allows the LCD device 2 to be viewed by the driver regardless of the basin-like arrangement of the LCD device 2 with respect to the surface of the dial assembly 3. The indicating needle 6 is a light-emitting needle made of a light-guide material such as transparent synthetic resin.
A plurality of the LED light sources 10 are provided on the front surface of the main board 4 such that the shaft 52 of the motor 5 is surrounded by the LED light sources 10. The prism 11 is provided between the LED light sources 10 and a light-entrance surface Mj of the indicating needle 6. The prism 11 is used to concentrate the light beams emitted by the LED light sources 10 to let the concentrated light beams enter the light-entrance surface Mj of the indicating needle 6. The light beams that entered the light-entrance surface Mj undergo five times of reflection by reflecting surfaces M21 to M25 in order of appearance (see FIG. 4) before reaching the needle portion 644. The light beams that entered the needle portion 644 are further reflected off a back surface of the needle portion 644 and then exit a front surface thereof. In this manner, the needle portion 644 is seen to emit light.
A drawback of the conventional display unit 1 is that it is necessary to arrange the plurality of LED light sources 10 around the shaft 52 in order to make the indicating needle 6 emit light, making it difficult to eliminate the irregular luminescence of the indicating needle 6 due to turning of the indicating needle. In the conventional display unit 1, the light beams emitted by the LED light sources 10 are concentrated using the prism 11 and enter the light-entrance surface Mj of the indicating needle 6 to increase brightness of the needle portion 644. This configuration introduces irregularity in luminescence during turning when there is not sufficient distance between the LED light source 10 and the light-entrance surface Mj lo of the indicating needle 6.
Apart from the problem of the needle's irregular luminescence, the conventional display unit 1 has another problem. Since a light beam emitted by the LED light source 10 travels via the five reflecting surfaces M21 to M25 before reaching the needle portion 644, multiple times of reflection causes considerable attenuation of light beams, making it difficult to obtain sufficient level of brightness or luminance of the needle portion 644.
Thus, the times of reflection of light beams inside of the indicating needle should be reduced. Also, it is preferable that leakage of light from surfaces of the indicating needle other than the top surface of the needle portion is effectively prevented. Further, if a structure designed to overcome the above-identified drawbacks is to be incorporated, it is appreciated that side effect or disadvantage caused by such a newly introduced structure should also be eliminated or minimized.
In view of the foregoing, it can be seen that a solution is needed which addresses these uneven and insufficient brightness issues so as to enable a manufacturer to provide improved functionality and appearance quality of in-vehicle display devices.